The present invention relates to a surface instability detection apparatus which permits testing samples of geomaterials under axial loads, and in particular, it relates to a surface instability detection apparatus which tests prismatic geomaterial specimens which are restrained and confined on all sides but one.
Surface instability testing of geomaterial, which, for purposes of this application is defined as including, but not limited to, rock and concrete, has been recognized as important in determination of geomaterial characteristics. Geological sample testing apparatus is known wherein what may be termed a selfsupporting geological sample, such as a core of a rock or compacted sand, is subjected to external forces by what is known as a tri-axial testing cell. Normally, hydraulic fluid is introduced in the annular space of a chamber surrounding the sample to apply a hydraulic pressure to the exterior cylindrical surface of the sample. An impermeable membrane usually surrounds the sample being arranged such that the membrane encloses the sample and seals the upper and lower platens to prevent hydraulic fluid gaining access to the ends of the sample.
Geological sample testing has been carried out in the prior art on substantially unrestrained cylindrical core samples in Bishop et al U.S. Pat. No. 3,505,860. The Bishop patent describes a geological sample testing apparatus which includes a chamber with a sample placed between a ram and a platen. A space is left around the sample into which hydraulic fluid is introduced to apply pressure to the sample.